The electric drive of an elevator attends to the moving of an elevator car in an elevator hoistway between stopping floors. The control system of the elevator forms a target value for the speed of the elevator car, i.e. a speed reference, for the electric drive. The speed reference can be divided into the acceleration phase of a run, the phase of even speed, and also the deceleration phase. The control system of the elevator starts the deceleration phase of a run when the elevator car has arrived at a predefined distance from the stopping floor. Normally the speed of the elevator car decelerates in a controlled manner at the deceleration determined by the speed reference such that the speed of the elevator car decreases to zero when the elevator car arrives at the stopping floor. The aim, especially when the elevator car stops at the terminal floor, is to ensure that the speed of the elevator car decelerates rapidly enough, because otherwise the elevator car or the counterweight is in danger of colliding with the end buffer. It is particularly important to ensure adequate deceleration when using so-called shallow end zones, such as a shallow pit of the elevator hoistway or shallow top clearance in the top part of the elevator hoistway. When using shallow end zones also the length of the end buffers, and therefore the collision damping capability, is usually limited. To ensure deceleration of the elevator car, the speed of an elevator car approaching the terminal floor is measured, and if the speed exceeds a set monitoring limit a mechanical stopping appliance, such as a safety gear, is activated to stop the elevator car. The aforementioned monitoring limit can be determined dependently on location such that the same value for the monitoring limit is always used in the same location and at the same distance from the end of the elevator hoistway.
A passenger in the elevator may find the gripping situation a quite unpleasant experience owing to the significantly greater than normal deceleration of the elevator car during the gripping. When the elevator is driving upwards, if the deceleration of the elevator car were to exceed the acceleration of free fall of the attractive force of the earth's gravity when the elevator is driving upwards, there would be the additional danger that an elevator passenger would rise into the air as a consequence of the gripping situation. Additionally, during an emergency stop of the elevator car the deceleration might vary in different parts of the elevator hoistway owing to, among other things, the effect of the weight of the elevator ropes. Elongation of the elevator ropes, on the other hand, might result in the speed of the elevator car during deceleration being momentarily greater than that permitted even if the speed of the traction sheave of the hoisting machine were to decelerate in the manner specified by the speed reference. Particularly with large travel heights, speed monitoring could activate the safety gear as a result of instantaneous overspeed caused by elongation of the elevator ropes.